Solenoid valve unit for fuel injection apparatus

ABSTRACT

A solenoid valve unit for a fuel injection apparatus suppresses fuel vaporization when the engine is being started or restarted when hot and enhances the reliability of engine operation by providing a stable fuel delivery during engine startup.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel injection apparatus, andparticularly to a solenoid valve unit for a fuel injection apparatus,and more particularly to a solenoid valve unit for a fuel injectionapparatus that provides appropriate control of cylinder fuel pressure ina gasoline injection system during engine stamp and normal engineoperation.

2. Prior Art Statement

With a conventional cylinder fuel injection system, when the engine hasbeen stopped and is restarted while still hot (i.e., a hot restart),problems have been caused by fuel (gasoline, for example) beingvaporized in the fuel piping owing to the high temperature in the enginecompartment. This has led to a demand for a system that can maintainstable fuel pressure and prevent fuel vaporization during a hot restart.In particular, when a high-pressure pump driven by the rotation of theengine is used to inject fuel, at low engine speeds the fuel injectionamount decreases, making it difficult to prevent fuel vaporizationduring a hot restart.

JPA 5-321782 discloses a fuel injection apparatus that is able tomaintain a constant pressure on the intake side of a high-pressure pumpby providing a pressure control valve between a high-pressure pump and alow-pressure pump, and returning fuel from an overflow valve in thehigh-pressure pump to the pressure control valve. Mechanical pressureflow control valves have been disclosed, such as, for example, by JPA60- 56872. These mechanical pressure valves are arranged so that fuel isinjected via a common rail when the pressure of the fuel being deliveredfrom the pump exceeds the force exerted by a valve spring.

An object of a first aspect of the invention is to provide a solenoidvalve unit for a fuel injection apparatus that suppresses fuelvaporization when an engine is subjected to a hot restart and reliablyimproves engine operation, by providing a stable fuel delivery when theengine is started.

A further object of the first aspect of the invention is to provide asolenoid valve unit for a fuel injection apparatus that can pump fuel atlow pressure when the engine is started and change over to high-pressuredelivery during normal engine operation.

A further object of the first aspect of the invention is to provide asolenoid valve unit for a fuel injection apparatus that can pump fuel atlow pressure when the engine is started and change over to high-pressuredelivery during normal engine operation, in which the cost can bereduced by using a single solenoid valve to comprise the solenoid valveunit.

A further object of the first aspect of the invention is to provide asolenoid valve unit for a fuel injection apparatus in which the timingof signals sent to a solenoid valve can be simplified and the solenoidvalve opened and closed with a small force, wherein once a controlsignal has been used to open the solenoid valve, the open state can bemaintained when the valve is receiving fuel delivered under highpressure without having to continue to supply control signals.

Further second, third and fourth aspects of the invention are describedfollowing the description of thee embodiments relating to the aboveaspects of the invention.

SUMMARY OF THE INVENTION

For achieving the above objects, the first aspect of the inventionprovides a solenoid valve unit for a fuel injection apparatus, said theapparatus comprising a low-pressure pump that supplies fuel at lowpressure from a fuel tank, a high-pressure pump that supplies thelow-pressure fuel from the low-pressure pump to an injector that injectsthe fuel at high pressure into an engine the solenoid valve unitcomprising, a housing provided with a high-pressure lead-in port fromthe injector, a low-pressure lead-out port to the fuel tank, a returnport from the high-pressure pump, a high-pressure passage incommunication with the lead-in port, a low-pressure passage incommunication with the lead-out port, and a return port passage incommunication with the return port, a pressure control valve that opensand closes the high-pressure passage and low-pressure passage inaccordance with pressure at the lead-in port, and solenoid valves ableto communicate with the lead-in port and lead-out port via the pressurecontrol valve and able to open and close communication between thehigh-pressure passage and the low-pressure passage, and between thelow-pressure passage and the return port passage, wherein the solenoidvalves are controlled to open communication between the high-pressurepassage and the low-pressure passage and close communication between thelow-pressure passage and the return port passage during engine startup,and close communication between the high-pressure passage and thelow-pressure passage, and open communication between the low-pressurepassage and the return port passage during normal engine operation.

The above solenoid valve unit can be provided with a first solenoidvalve that opens and closes communication between the high-pressurepassage and the low-pressure passage and a second solenoid valve thatopens and closes communication between the low-pressure passage and thereturn port passage.

In the above solenoid valve unit, moreover, after the engine isoperating normally communication between the high-pressure passage andthe low-pressure passage can be closed by setting the first solenoidvalve off and communication between the low-pressure passage and thereturn port passage can be opened by setting the second solenoid valveto off. Also, after the engine is operating normally, communicationbetween the high-pressure passage and the low-pressure passage is closedby setting the first solenoid valve to on and communication between thelow-pressure passage and the return port passage is opened by settingthe second solenoid valve to off.

The solenoid valve can use a single armature to drive a first valveelement that opens and closes communication between the high-pressurepassage and the low-pressure passage and a second valve element thatopens and closes communication between the low-pressure passage and thereturn port passage. Also, after the engine is operating normally,communication between the high-pressure passage and the low-pressurepassage can be closed and communication between the low-pressure passageand the return port passage opened by setting the solenoid valve to on.

In the solenoid valve unit for a fuel injection apparatus according tothis first aspect of the invention, at the time of engine startupcommunication is opened between the low-pressure passage andhigh-pressure passage while at the same time closing communicationbetween the low-pressure passage and the return port passage. There istherefore rise in the pressure acting on the pressure control valve onthe high-pressure pump side, so there is no high-pressure delivery offuel by the high-pressure pump, allowing fuel to be supplied at lowpressure to the injector from the low-pressure pump. Furthermore, duringnormal engine operation communication between the high-pressure passageand the low-pressure passage is closed while at the same timecommunication is opened between the low-pressure passage and the returnport passage, whereby the high-pressure pump pressure increases,enabling normal high-pressure fuel delivery to take place.

That is, the characteristic of the low-pressure pump is used, the factthat the delivery pressure is low but that the delivery flow amount issufficient when starting the engine. When the engine is being started, afuel supply circuit is switched to nullify the high-pressure pump orstop fuel pressurization by the pump, thereby allowing the fuel to bedelivered to the injector using just the low-pressure pump, which canprovide enough fuel for starting the engine. Thus, it becomes possibleto suppress fuel vaporization during a hot restart and the like. Afterthe engine has been started and is operating normally, a switchover bythe solenoid valve enables normal high-pressure fuel delivery from thehigh-pressure pump to take place.

After the engine is operating normally, by setting the solenoid valve toon so that communication between the high-pressure passage and thelow-pressure passage is closed, the solenoid valve is also subjected,via the pressure control valve, to the pressure of the fuel suppliedunder high-pressure from the high-pressure pump. As the communicationbetween the high-pressure passage and low-pressure passage thereforeremains closed even if the solenoid valve is set to off, control signalsto the solenoid valve can be simplified. Also, as the solenoid does nothave to be energized as long as exposure to the high-pressure fuelcontinues, it is possible to employ a less powerful solenoid valve.

Using a single armature to drive both a first valve element that opensand closes communication between the high-pressure passage and thelow-pressure passage and a second valve element that opens and closescommunication between the low-pressure passage and the return portpassage, makes it possible to effect the above control with a singlesolenoid valve. This can contribute to reducing the size, complexity andcost of the structure.

The above and other features of the present invention will becomeapparent from the following description made with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a fuel injection apparatus 1 equippedwith a solenoid valve unit 2 in a first embodiment according to thefirst aspect of the invention.

FIG. 2 is a sectional view of the above solenoid valve unit 2.

FIG. 3 is a chart showing the operating states of the various elementsof the solenoid valve unit.

FIG. 4 is a graph showing the relationship between engine speed and thepressure of fuel to the injector 6A.

FIG. 5 is a sectional view of a solenoid valve unit 50 in a secondembodiment according to the first aspect of the invention.

FIG. 6 is a chart showing the operating states of the various elementsof the above solenoid valve unit.

FIG. 7 is a schematic diagram of a fuel injection apparatus equippedwith a solenoid valve unit 60 in a third embodiment according to thefirst aspect of the invention.

FIG. 8 is a sectional view of the above solenoid valve unit 60 that usesa single solenoid valve 62.

FIG. 9 is a chart showing the operating states of the various elementsof the above solenoid valve unit.

FIG. 10 is a graph showing the relationship between engine speed and thepressure of fuel to the injector 6A.

FIG. 11 is a schematic diagram of a fuel injection apparatus 140equipped with a solenoid valve unit 141 in a fourth embodiment accordingto the second aspect of the invention.

FIG. 12 is a sectional view of the above solenoid valve unit 141.

FIG. 13 is a is a chart showing the operating states of the variouselements of the above solenoid valve unit.

FIG. 14 is a graph showing the relationship between engine speed and thepressure of fuel to the injector 6A.

FIG. 15 is a schematic diagram of a fuel injection apparatus 155equipped with a solenoid valve unit 156 in a fifth embodiment accordingto the third aspect of the invention.

FIG. 16 is a sectional view of the above solenoid valve unit 156.

FIG. 17 is a schematic diagram of a fuel injection apparatus equippedwith a solenoid valve unit 160 in a sixth embodiment according to thefourth aspect of the invention.

FIG. 18 is a schematic diagram of a fuel injection apparatus equippedwith a solenoid valve unit 170 in a seventh embodiment according to thefourth aspect of the invention.

FIG. 19 is a sectional view of the principal parts of a solenoid valveunit of the fourth aspect of the invention in which a flat plate shapedvalve element 176 is used.

FIG. 20 is a graph showing the relationship between flow amount andcontrol pressure on the solenoid valve in the above arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the solenoid valve unit for a fuel injectionapparatus according to the first aspect of the invention will now bedescribed with reference to FIGS. 1 to 4. FIG. 1 is a schematic diagramof a solenoid valve unit 2 for a fuel injection apparatus 1, in which hefuel injection apparatus 1 is provided with a fuel tank 3, alow-pressure feed pump (low-pressure pump) 4, a high-pressure gasolinepump (high-pressure pump) 5, a common rail (accumulator) 6, an injector6A and the solenoid valve unit 2.

The low-pressure pump 4 is electrically driven and therefore does notdepend on the speed (revolutions per minute) of the engine (not shown).The delivery flow amount of the low-pressure pump 4 is thereforeconstant, regardless of the engine speed. The driving of thehigh-pressure pump 5 is related to the engine, so an amount of fuelcorresponding to the engine speed can be fed under high pressure to thecommon rail 6, and therefore to the injector 6A.

The solenoid valve unit 2 is provided with a high-pressure control valve7, a first solenoid valve 8 and a second solenoid valve 9. Thehigh-pressure control valve 7 and the first solenoid valve 8 areconnected in parallel between a high-pressure lead-in port 10 and alow-pressure lead-out port 11 of the high-pressure control valve 7.Also, the high-pressure control valve 7 and the second solenoid valve 9are connected in parallel between the high-pressure pump 5 and thelow-pressure lead-out port 11. A return port 12 from the high-pressurepump 5 is connected to the second solenoid valve 9. The solenoid valveunit 2 is also provided with a control circuit 13 for the first solenoidvalve 8 and second solenoid valve 9.

FIG. 2 is a partial sectional view of the solenoid valve unit 2. Thehigh-pressure control valve 7, first solenoid valve 8 and secondsolenoid valve 9 of the solenoid valve unit 2 are arranged in a valveunit housing 20. The high-pressure lead-in port 10, low-pressurelead-out port 11 and return port 12 are formed in the housing 20. Thehigh-pressure control valve 7 intersects a high-pressure passage 21 thatcommunicates with the high-pressure lead-in port 10 and a low-pressurepassage 22 that communicates with the low-pressure lead-out port 11. Apressure control valve element 23 seats on a valve seat member 24. Thehigh-pressure passage 21 and low-pressure passage 22 are maintained in aclosed state by a control spring 25 urging the valve element 23 closed.

When the pressure from the high-pressure lead-in port 10 becomesexcessively high, the valve element 23 is lifted off the valve seatmember 24 against the resistance of the spring 25, the gap between thevalve element 23 and valve seat member 24 thus forming a passage 26(indicated in the drawing by a phantom line) between the high-pressurepassage 21 and low-pressure passage 22. The high-pressure control valve7 may also be constituted as a spool type valve.

The first solenoid valve 8 is able to communicate with the high-pressurelead-in port 10 and low-pressure lead-out port 11 via the high-pressurecontrol valve 7. For this, a valve element 28 that seats on a valve seatmember 27 between the high-pressure passage 21 and the low-pressurepassage 22 is normally urged onto the valve seat member 27 by a solenoidspring 31 provided between an armature 29 integrated with the valveelement 28 and a spring seat member 30. Energizing a solenoid 32 by asignal from the control circuit 13 causes the armature 29 to be drawn inagainst the resistance of the solenoid spring 31, lifting the valveelement 28 from the valve seat member 27 and opening communicationbetween the high-pressure passage 21 and the low-pressure passage 22.When the pressure from high-pressure lead-in port 10 has reached asufficiently high level, the state of open communication is maintained.

The second solenoid valve 9 is able to communicate with thehigh-pressure lead-in port 10 and low-pressure lead-out port 11 via thehigh-pressure control valve 7. For this, there is a valve element 35that seats on a valve seat member 34 located between the low-pressurepassage 22 and a return port passage 33 that communicates with thereturn port 12. Provided between an armature 36 integrated with thevalve element 35 and a spring seat member 37 is a solenoid spring 38,and there is also a valve spring 40 between the valve element 35 and aspring seat member 39. The force of the spring 38 urges the valveelement 35 towards the valve seat member 34, opening a space between thevalve element 35 and the valve seat member 34 that allows communicationbetween the low-pressure passage 22 and the return port passage 33. Byenergizing a solenoid 41 with a signal from the control circuit 13, thearmature 36 is drawn in against the resistance of the solenoid spring38, seating the valve element 35 on the seat 34 thereby closingcommunication between the low-pressure passage 22 and the return portpassage 33.

The operating states of the elements in the solenoid valve unit 2 thusconfigured is shown in FIG. 3, and will now be described, with referencealso to the graph of FIG. 4 showing the relationship between enginespeed and fuel pressure. Setting the first solenoid valve 8 on duringengine startup causes the valve element 28 to be lifted from the valveseat member 27. This opens the high-pressure passage 21, openingcommunication between the high-pressure passage 21 and the low-pressurepassage 22. By also setting the second solenoid valve 9 to on, the valveelement 35 is seated on valve seat member 34, closing the return portpassage 33, thereby closing communication between the low-pressurepassage 22 and the return port passage 33.

With communication thus opened between the high-pressure passage 21 andthe low-pressure passage 22 by the first solenoid valve 8, there is norise in pressure in the passage 21 and fuel pressure at the injector 6Ais low, making it possible to start the engine with the low pressurefuel delivery of the low-pressure pump 4. Also, with communication thusclosed between the low-pressure passage 22 and the return port passage33 by the second solenoid valve 9, there is a large flow of low-pressurefuel in the fuel piping, delivered at a constant rate from thelow-pressure pump 4, that fills the piping, suppressing fuelvaporization. The cooling and lubrication of the high-pressure pump 5are effected by the large flow of fuel from the low-pressure pump 4.

Reverting to FIG. 3, once the engine is running normally the firstsolenoid valve 8 can be switched off, which closes communication betweenhigh-pressure passage 21 and low-pressure passage 22 by seating thevalve element 28 on the valve seat member 27. As a result, high pressureis produced in the high-pressure passage 21 and at the injector 6A, andhigh-pressure injection is carried out using the high-pressure pump 5.When the second solenoid valve 9 is switched off the valve element 35 islifted off the valve seat member 34, which opens communication betweenthe low-pressure passage 22 and the return port passage 33, allowingnormal cooling and lubrication of the high-pressure pump 5

With respect to changes over time in the pressure of fuel going to theinjector 6A and the engine speed, as shown in FIG. 4, when the key isturned to the accessory on position (not shown), the low-pressure pump 4is activated, raising the fuel pressure. The engine is cranked byturning the key further, to the ignition on position (not shown). Untilthe key is turned to the ignition on position, the first solenoid valve8 is closed and the second solenoid valve 9 is open, or the firstsolenoid valve 8 and second solenoid valve 9 are both open, and when theignition is switched on, as described above, the first solenoid valve 8is opened and the second solenoid valve 9 is closed, and the engine isstarted using low-pressure fuel delivery by the low-pressure pump 4.

After the engine is fully operational, engine speed is increased byclosing the first solenoid valve 8 and opening the second solenoid valve9, whereby fuel pressure rises for normal operation under high-pressurefuel delivery. When the key is turned to the off position, the firstsolenoid valve 8 closes and the second solenoid valve 9 opens, or valves8 and 9 are both opened. As the first solenoid valve 8 is configured asa high-pressure opposition type valve, meaning it has to be held closedagainst pressure from the high-pressure passage 21, it is necessary touse a powerful solenoid 32.

A second embodiment of the solenoid valve unit according to the firstaspect of the invention will now be described with reference to FIGS. 5and 6. FIG. 5 is a sectional view of a solenoid valve unit 50 of thesecond embodiment. The difference between the solenoid valve unit 50 andsolenoid valve unit 2 is that instead of the first solenoid valve 8, thesolenoid valve unit 50 has a first solenoid valve 51 having the sameconfiguration as the second solenoid valve 9. Parts of the 51 havetherefore been given the same reference numerals as those of the secondsolenoid valve 9, and further explanation thereof is omitted.

Setting the first solenoid valve 51 off during engine startup causes thevalve element 35 to be lifted from the valve seat member 34, openingfirst solenoid valve 51. This opens the high-pressure passage 21, thatis, communication is opened between high-pressure passage 21 andlow-pressure passage 22. The second solenoid valve 9 is also set to on,which seats the valve element 35 on the valve seat member 34, closingthe second solenoid valve 9 and thereby the return port passage 33,meaning that communication between the low-pressure passage 22 and thereturn port passage 33 is closed. As the first solenoid valve 51 isopen, the engine can be started using the low-pressure fuel delivery ofthe low-pressure pump 4, without using the high-pressure pump 5.

Reverting to FIG. 6, once the engine is operating normally, the firstsolenoid valve 51 is closed by switching it on, closing high-pressurepassage 21 and the second solenoid valve 9 is opened by switching itoff, opening return port passage 33, resulting in high-pressure fuelinjection by the high-pressure pump 5.

The first solenoid valve 51 is a high-pressure action type. Therefore,once the engine is operating normally under high-pressure fuelinjection, even if the first solenoid valve 51 is switched off, becausethe fuel pressure from the high-pressure lead-in port 10 is sufficientlyhigh, the valve element 35 remains seated on the valve seat member 34against the resistance of the solenoid spring 38, maintaining the closedstate of the high-pressure passage 21. This allows fuel to be deliveredunder high pressure by the high-pressure pump 5 and also improves thehigh-pressure retention characteristics. This simplifies control signalsto the solenoid 41 of the first solenoid valve 51. Compared with thefirst solenoid valve 8, another improvement is that a less powerfulsolenoid 41 can be used.

After the engine has been stopped, the first solenoid valve 51 isswitched off, reopening high-pressure passage 21, and the secondsolenoid valve 9 is switched off, opening return port passage 33. Thesolenoid valve unit 2 of the first embodiment and the solenoid valveunit 50 of the second embodiment both require a first solenoid valve 8or 51 and a second solenoid valve 9, but the solenoid valve unitaccording to this first aspect of the invention can also be configuredusing a single solenoid valve.

A third embodiment of the first aspect of the invention that uses asingle solenoid valve will now be described with reference to FIGS. 7 to10. FIG. 7 is a schematic diagram of a fuel injection apparatus 1equipped with a solenoid valve unit 60 according to the third embodimentof the invention, and FIG. 8 is a sectional view of the solenoid valveunit 60. With reference to the drawings, in addition to the solenoidvalve unit 60, the fuel injection apparatus 1 is provided with a fueltank 3, low-pressure pump 4, high-pressure pump 5, common rail 6,injector 6A and high-pressure control valve 7.

A high-pressure control valve 7 and a single solenoid valve 62 areprovided in a housing 61 of the solenoid valve unit 60. The housing 61also has a high-pressure lead-in port 10, a low-pressure lead-out port11, a return port 12, and a solenoid valve 62 control circuit 13. Thehigh-pressure control valve 7 and the solenoid valve 62 are connected inparallel between the high-pressure lead-in port 10 and the low-pressurelead-out port 11, and the return port 12 from the high-pressure pump 5is connected to the solenoid valve 62. The solenoid valve 62 straddleshigh-pressure passage 21, low-pressure passage 22 and return portpassage 33, and is provided with an armature 36, a spring seat member37, solenoid spring 38, spring seat member 39, valve spring 40, solenoid41, first valve element 63, connecting rod 64, second valve element 65and a valve seat member 66.

The first valve element 63, connecting rod 64 and second valve element65 are integrated with the armature 36. The first valve element 63 seatson a first seat face 66A of the valve seat member 66, and the secondvalve element 65 seats on a second seat face 66B. A connecting passage66C is formed in the valve seat member 66 that is able to providecommunication between the high-pressure passage 21 and low-pressurepassage 22, and between the return port passage 33 and low-pressurepassage 22.

The operating states of the elements in the solenoid valve 62 thusconfigured is shown in FIG. 9, and will now be described, with referencealso to the graph of FIG. 10 showing the relationship between enginespeed and fuel pressure. Setting the solenoid valve 62 off during enginestartup causes the first valve element 63 to be lifted from the seatface 66A. This opens the high-pressure passage 21, opening communicationbetween the high-pressure passage 21 and the low-pressure passage 22,and seats the second valve element 65 on the second seat face 66B,closing the return port passage 33, thereby closing communicationbetween the return port passage 33 and the low-pressure passage 22.

With communication thus opened between the high-pressure passage 21 andthe low-pressure passage 22, there is no rise in pressure in the passage21, so fuel pressure at the common rail 6 and injector 6A is low, makingit possible to start the engine with the low pressure fuel deliveryprovided by low-pressure pump 4. Reverting to FIG. 9, once the enginehas been started and is running normally under high-pressure fuelinjection, the solenoid valve 62 is switched on to close communicationbetween the high-pressure passage 21 and low-pressure passage 22 byseating the valve element 63 on the seat face 66A. Also, the secondvalve element 65 is lifted from the second seat face 66B, openingcommunication between return port passage 33 and low-pressure passage22, and with communication between high-pressure passage 21 andlow-pressure passage 22 being closed, high pressure is produced in thehigh-pressure passage 21 and at the injector 6A, and high-pressureinjection by the high-pressure pump 5 takes place.

With respect to the pressure of fuel supplied to the common rail 6 andinjector 6A and the engine speed, as shown in FIG. 10, when the key isturned to the accessory on position (not shown), the low-pressure pump 4is activated, raising the fuel pressure. The engine is cranked byturning the key further, to the ignition on position (not shown). Untilthe key is turned to the ignition on position, communication between thehigh-pressure passage 21 and the low-pressure passage 22 is open andcommunication between the return port passage 33 and low-pressurepassage 22 is closed. Turning the key to the ignition on position causesthe engine to be started with the low-pressure fuel delivery by thelow-pressure pump 4.

As described above, communication can be closed between thehigh-pressure passage 21 and low-pressure passage 22 and opened betweenthe return port passage 33 and low-pressure passage 22 by setting thesolenoid valve 62 on, and as the solenoid valve 62 is a high-pressureaction type, even if the solenoid valve 62 is switched off, the closedcommunication between the high-pressure passage 21 and low-pressurepassage 22 and the open communication between the return port passage 33and the low-pressure passage 22 can be maintained, making it possible tosimplify control signals to the solenoid 41 (see the control signal tothe solenoid 41 in FIG. 10) and to shorten the time electrical power isapplied to the solenoid 41. After the low-pressure start, closingcommunication between the high-pressure passage 21 and the low-pressurepassage 22 and opening communication between the return port passage 33and the low-pressure passage 22 increases the engine speed and fuelpressure, for normal engine operation by high-pressure fuel injection.When the key is turned to the off position, communication is openedbetween high-pressure passage 21 and low-pressure passage 22 and closedbetween return port passage 33 and low-pressure passage 22.

With the solenoid valve unit 60 thus configured, communication betweenlow-pressure passage 21 and return port passage 33 can be opened andclosed by means of a single solenoid valve 62 (single solenoid 41),which contributes to reducing the cost.

After the engine has been started and is operating normally withhigh-pressure fuel injection, even if the first solenoid valve 62 isswitched off, because the fuel pressure from the high-pressure lead-inport 10 is sufficiently high (the solenoid valve 62 being configured asa high-pressure action type in which the high-pressure fuel acts in thedirection in which the first valve element 63 is seated), the firstvalve element 63 remains seated on the first seat face 66A against theresistance of the solenoid spring 38, so communication between thehigh-pressure passage 21 and the low-pressure passage 22 remains closed.This allows fuel to be delivered under high pressure by thehigh-pressure pump 5 and also improves the high-pressure retentioncharacteristics. It is therefore possible to simplify control signals tothe solenoid 41 (see the control signal to the solenoid 41 in FIG. 10)and to shorten the time electrical power is applied to the solenoid 41,and a less powerful solenoid 41 can be used.

After the engine has been stopped, as shown in FIG. 9, communication canbe opened between high-pressure passage 21 and low-pressure passage 22and closed between return port passage 33 and low-pressure passage 22 byswitching off the solenoid valve 62. That is, once the engine has beenoperating under high-pressure fuel injection, the fuel pressure cannotbe lowered until the engine has been stopped. Therefore, withcommunication remaining closed between the high-pressure passage 21 andlow-pressure passage 22 and communication remaining open between thereturn port passage 33 and low-pressure passage 22, when duringtransmission (not shown) changes or the like the engine speed is reducedwithout being able to change over from the high-pressure pump 5 to thelow-pressure pump 4, the delivery amount of the high-pressure pump 5decreases, and can result in engine stoppage.

Thus, what is desirable is to be able to ensure a prescribedlow-pressure flow amount by the low-pressure pump 4 after the engine hasbeen started and is running at a very low speed, and the ability, evenduring normal engine operation, to change between high-pressure andlow-pressure fuel injection modes in accordance with engine runningrequirements. Furthermore, the solenoid valve unit 60 requires ahigh-pressure control valve 7 and a separate high-pressure changeoversolenoid valve 62, which makes it difficult to reduce the cost of theparts, the overall size and the number of assembly steps, and also makesit difficult to improve the reliability.

These problems and matters are addressed by second, third and fourthaspects of the invention, the object of which also is to provide asolenoid valve unit for a fuel injection apparatus that suppresses fuelvaporization when an engine is subjected to a hot restart and reliablyimprove engine operation, by providing a stable fuel delivery when theengine is started.

A further object of the second, third and fourth aspects of theinvention is to provide a solenoid valve unit for a fuel injectionapparatus that can pump fuel at low pressure when the engine is startedand change over to high-pressure delivery during normal engineoperation.

A further object of the second, third and fourth aspects of theinvention is to provide a solenoid valve unit for a fuel injectionapparatus that can pump fuel at low pressure when the engine is startedand change over to high-pressure delivery during normal engineoperation, in which the cost can be reduced by using a single solenoidvalve to comprise the solenoid valve unit.

Moreover, while the first three embodiments according to the firstaspect of the invention are also directed at resolving the difficulty,during a hot restart, of eliminating air, insufficiency of the fuelinjection amount when the engine is being started or is operating atvery low speeds, pressure instability of high-pressure fuel delivery andother such problems, the following embodiments according to the second,third and fourth aspects of the invention provide a further improvementto resolve such problems. To achieve this object, a solenoid valve unitfor a fuel injection apparatus is provided that uses a magnetic valve(on/off valve) to ensure a prescribed low-pressure fuel delivery by alow-pressure feed pump after the engine has been started and is runningat very low speed, and is able, even during normal engine operation, tochange between high-pressure and low-pressure fuel injection modes inaccordance with engine running requirements.

A further object of the second, third and fourth aspects of theinvention is to provide a solenoid valve unit for a fuel injectionapparatus in which the solenoid valve unit is a high-pressure oppositiontype in which the direction in which the solenoid valve element isseated is opposite to the direction of high-pressure fuel delivery,enabling simplification of solenoid valve control signals.

A further object of the second, third and fourth aspects of theinvention is to provide a solenoid valve unit for a fuel injectionapparatus in which the high-pressure control valve and the high-lowpressure changeover solenoid valve are integrated to simplify thesolenoid valve unit and reduce the cost.

For achieving the above objects, the second aspect of the inventionprovides a fuel injection apparatus, including solenoid valve unit for afuel injection apparatus, the apparatus comprising a low-pressure pumpthat supplies fuel at low pressure from a fuel tank, a high-pressurepump that supplies the low-pressure fuel from the low-pressure pump toan injector that injects the fuel at high pressure into an engine thesolenoid valve unit comprising, a unit housing provided with ahigh-pressure lead-in port from the injector, a low-pressure lead-outport to the fuel tank, a high-pressure passage in communication with thelead-in port, and a low-pressure passage in communication with thelead-out port, a high-pressure control valve that opens and closes thehigh-pressure passage and low-pressure passage in accordance withpressure at the lead-in port, a solenoid valve that is able tocommunicate with the lead-in port and lead-out port via thehigh-pressure control valve and can open and close communication betweenthe high-pressure passage and the low-pressure passage, a check valvearranged between the low-pressure passage and the fuel tank, and alow-pressure control valve arranged between the high-pressure pump andthe fuel tank, wherein an opening pressure of the low-pressure controlvalve is set at a higher pressure than the opening pressure of the checkvalve and the solenoid valve is controlled to open communication betweenthe high-pressure passage and the low-pressure passage during enginestartup, and to close communication between the high-pressure passageand the low-pressure passage during normal engine operation.

The above objects are also achieved by a solenoid valve unit for a fuelinjection apparatus according to the third aspect of the invention,wherein, instead of the check valve used in the second aspect of theinvention, an orifice is formed in the high-pressure passage to set thepressure therein. The apparatus comprises a low-pressure pump thatsupplies fuel at low pressure from a fuel tank, a high-pressure pumpthat supplies the low-pressure fuel from the low-pressure pump to aninjector that injects the fuel at high pressure into an engine. Thesolenoid valve unit comprises a unit housing provided with ahigh-pressure lead-in port from the injector, a low-pressure lead-outport to the fuel tank, a high-pressure passage in communication with thelead-in port, and a low-pressure passage in communication with thelead-out port, said high-pressure passage having an orifice formedtherein, a high-pressure control valve that opens and closes thehigh-pressure passage and low-pressure passage in accordance withpressure at the lead-in port, a solenoid valve that is able tocommunicate with the lead-in port and lead-out port via thehigh-pressure control valve and can open and close communication betweenthe high-pressure passage and the low-pressure passage, and alow-pressure control valve arranged between the high-pressure pump andthe fuel tank, wherein the orifice in the high-pressure passage is of adiameter that allows the valve opening pressure of the low-pressurecontrol valve to be set at a higher pressure than the pressure in thehigh-pressure passage when the solenoid valve is set at open and thesolenoid valve is controlled to open communication between thehigh-pressure passage and the low-pressure passage during enginestartup, and to close communication between the high-pressure passageand the low-pressure passage during normal engine operation.

In a solenoid valve unit for a fuel injection apparatus according to thefourth aspect of the invention, a high-pressure control valve and asolenoid valve for switching high and low pressure are integrated. Theapparatus comprises a low-pressure pump that supplies fuel at lowpressure from a fuel tank, a high-pressure pump that supplies thelow-pressure fuel from the low-pressure pump to an injector that injectsthe fuel at high pressure into an engine. The solenoid valve unitcomprises a unit housing provided with a high-pressure lead-in port fromthe injector, a low-pressure lead-out port to the fuel tank, ahigh-pressure passage in communication with the lead-in port, and alow-pressure passage in communication with the lead-out port, ahigh-pressure control valve that opens and closes the high-pressurepassage and low-pressure passage in accordance with pressure at thelead-in port, and a solenoid valve that can open and close communicationbetween the high-pressure passage and the low-pressure passage, whereinthe solenoid valve and the high-pressure control valve are integrated bymaking common use of a valve element thereof.

The above high-pressure control valve, solenoid valves, check valve andorifice can be formed in a single unit housing. A damper portion can beformed on the low-pressure side or the high-pressure side of thehigh-pressure control valve, and the solenoid valve and pressure controlvalve element can be configured as flat plate shaped bodies.

In the solenoid valve units according to the second, third and fourthaspects of the invention, at the time of engine startup communication isopened between the low-pressure passage and high-pressure passage, as inthe first aspect of the invention. There is therefore no rise in thepressure acting on the pressure control valve on the high-pressure pumpside, so there is no high-pressure delivery of fuel by the high-pressurepump, allowing fuel to be supplied at low pressure to the common railand injector by the low-pressure pump. Communication between thehigh-pressure passage and the low-pressure passage is closed duringnormal engine operation, enabling normal high-pressure fuel delivery totake place.

Thus, the characteristic of the low-pressure pump is used, the fact thatthe delivery pressure is low but that the delivery flow amount issufficient when starting the engine. When the engine is being started, afuel supply circuit is switched to nullify the high-pressure pump orstop fuel pressurization by the pump, thereby allowing the fuel to bedelivered to the injector using just the low-pressure pump, which canprovide enough fuel for starting the engine. Thus, it becomes possibleto suppress fuel vaporization during a hot restart and the like. Afterthe engine is firing fully after startup, a switchover by the solenoidvalve enables normal high-pressure fuel delivery from the high-pressurepump to take place.

In the case of the arrangement according to the second aspect of theinvention using a check valve, as the opening pressure of thelow-pressure control valve of the high-pressure pump is set at a higherpressure than the check valve opening pressure, the above-describedeffects can be realized when the engine is being started and at very lowengine speeds. During normal engine operation, also, by switching thesolenoid on and off in accordance with the engine operating status, thecheck valve, i.e. the solenoid valve, can be opened and shut while thelow-pressure control valve remains closed, enabling the low-pressurepump to deliver the required amount during low speed operation withoutstopping the engine, thus realizing a stable supply of fuel.

In the case of the arrangement according to the third aspect of theinvention that instead of the check valve of the second aspect of theinvention uses an orifice formed in the high-pressure passage, the sizeof the orifice can be set at a desired diameter whereby when thesolenoid valve is open (on), the opening pressure of the low-pressurecontrol valve is higher than the high-pressure passage pressure, therebyproviding the same effect as the check valve arrangement according tothe second aspect of the invention.

The configuration according to the fourth aspect of the invention inwhich the high-pressure control valve and solenoid valve are integratedenables switching between low pressure and high pressure to be effectedby the operation of a single valve element reducing the cost and size ofthe arrangement and improving the reliability.

A fourth embodiment of the solenoid valve unit for a fuel injectionapparatus according to the second aspect of the invention will now bedescribed with reference to FIGS. 11 to 14. Parts that are the same asthose used in FIGS. 1 to 10 have been given the same reference numerals,further explanation thereof is omitted. FIG. 11 is a schematic diagramof a solenoid valve unit 141 of a fuel injection apparatus 140. Inaddition to the solenoid valve unit 141, the fuel injection apparatus140 is provided with a fuel tank 3, low-pressure pump 4, high-pressurepump 5, low-pressure control valve 142 for the high-pressure pump 5,common rail 6 and injector 6A. The common rail 6 is connected to theinjector 6A via a first bank rail 6B and second bank rail 6C having asmaller capacity.

The solenoid valve unit 141 is provided with a solenoid valve 143 havingan orifice 145, the high-pressure control valve 7, a check valve 144,and a return connection point 147 from the check valve 144 via alow-pressure lead-out port 146. The high-pressure control valve 7 andsolenoid valve 143 are provided in parallel between the high-pressurelead-in port 10 and the low-pressure lead-out port 146, and the checkvalve 144 in series.

FIG. 12 is a sectional view of the solenoid valve unit 141; thehigh-pressure control valve 7 has substantially the same configurationas the valve 7 of FIGS. 2, 5 and 8. The check valve 144 is arrangeddownstream of the low-pressure passage 22. The solenoid valve 143straddles the high-pressure passage 21 and the low-pressure passage 22,and is provided with an armature 148, a spring seat member 149, asolenoid spring 150, a solenoid 151, a valve seat member 152 and a valveelement 153. The valve element 153 is formed as an integral part of thearmature 148. The valve element 153 seats on a seat face 152A of thevalve seat member 152. The valve seat member 152 has a passage 152B thatcan provide communication between the high-pressure passage 21 and thelow-pressure passage 22, via the orifice 145. The opening pressure ofthe low-pressure control valve 142 is greater than that of the checkvalve 144.

The operating states of the elements in the solenoid valve unit 141 thusconfigured is shown in FIG. 13, and will now be described, withreference also to the graph of FIG. 14 showing the relationship betweenengine speed and fuel pressure. Setting the solenoid valve 143 on duringengine startup causes the valve element 153 to be lifted from the face152A of the valve seat member 152, opening communication between thehigh-pressure passage 21 and the low-pressure passage 22, as indicatedin FIG. 13. Because the opening pressure of the low-pressure controlvalve 142 is greater than that of the check valve 144, the low-pressurecontrol valve 142 is closed.

With communication thus opened between the high-pressure passage 21 andthe low-pressure passage 22, there is no rise in pressure in the passage21, resulting in low fuel pressure at the common rail 6 and injector 6Aof FIG. 11, making it possible to start the engine with the low-pressurefuel delivery provided by low-pressure pump 4 (refer to the "Pump Used"column in FIG. 13). The large flow of low-pressure fuel delivered at aconstant rate by the low-pressure pump 4 fills the fuel piping,suppressing fuel vaporization. The cooling and lubrication of thehigh-pressure pump 5 are effected by the large flow of fuel from thelow-pressure pump 4.

Reverting to FIG. 13, once the engine has been started and is runningnormally under high-pressure fuel injection, the solenoid valve 143 isswitched off to close communication between the high-pressure passage 21and low-pressure passage 22 by seating the valve element 153 on the seatface 152A. As a result, high pressure is produced in the high-pressurepassage 21 and at the common rail 6 and injector 6A, and high-pressureinjection by the high-pressure pump 5 takes place. Switching thesolenoid valve 143 off causes the pressure to rise in the high-pressurepassage 21, resulting in high pressure at the common rail 6 and injector6A. Opening the low-pressure control valve 142 allows normal cooling andlubrication by the fuel of the high-pressure pump 5.

With respect to changes over time in the pressure of fuel going to thecommon rail 6 and injector 6A and the engine speed, as shown by FIG. 14,when the key is turned to the accessory on position (not shown), thelow-pressure pump 4 is activated and raises the fuel pressure. Theengine is cranked by turning the key further, to the ignition onposition (not shown). Until the key is turned to the ignition onposition, communication between the high-pressure passage 21 andlow-pressure passage 22 is open and the low-pressure control valve 142closed. When the ignition is switched on, as described above, the engineis started using low-pressure fuel delivery by the low-pressure pump 4.

Switching the solenoid valve 143 over from on to off allowscommunication to be closed between the high-pressure passage 21 andlow-pressure passage 22, and the low-pressure control valve 142 to beopened. Turning the key to the off position closes communication betweenthe high-pressure passage 21 and low-pressure passage 22 and closes thelow-pressure control valve 142. As the check valve 144 is locateddownstream of the solenoid valve 143 and high-pressure control valve 7,a prescribed low pressure can be maintained even after the engine hasstopped.

A high-pressure opposition type valve configuration is used in which thevalve element 153 is urged onto the seat face 152A against the highpressure, to close the high-pressure passage 21. Therefore, only twocontrol stages are required, to switch the solenoid valve 143 on whenthe engine is being started, and switch the solenoid valve 143 off whenthe engine is operating normally. Compared to the three-stage control ofthe solenoid valve unit 60 (FIGS. 7 to 10) consisting of switching itoff at engine startup, on after the engine is fully operational, and offagain when the engine is operating normally, rather than not functioninguntil the engine is stopped, control is simpler, with the valve element153 functioning as soon as the solenoid valve 143 is switched off.

Moreover, as shown by FIG. 13, even after the engine has started up andis running normally, during low-pressure operation in particular, whenthe solenoid valve 143 is switched from off to on the valve element 153immediately becomes operational. Switching the solenoid valve 143 oncauses the valve element 153 to be lifted from the seat face 152A,opening communication between the high-pressure passage 21 andlow-pressure passage 22, as at engine startup time. As the check valve144 has a lower opening pressure than that of the low-pressure controlvalve 142, the low-pressure control valve 142 remains closed, so aprescribed amount of fuel is supplied to the common rail 6 and injector6A not by the high-pressure pump 5, but instead by the low-pressure pump4.

By giving the orifice 145 communicating with the high-pressure passage21 a prescribed diameter that causes the opening pressure at which thelow-pressure control valve 142 is set to exceed the high-pressurepassage 21 pressure when the solenoid valve 143 is on (open), the needfor the check valve 144 is eliminated. This will now be described withreference to a fifth embodiment of a solenoid valve unit 156 for a fuelinjection apparatus 155 according to the third aspect of the invention,as shown in FIG. 15 and the sectional view of the solenoid valve unit156 shown in FIG. 16. In addition to the solenoid valve unit 156, thefuel injection apparatus 155 is provided with a fuel tank 3,low-pressure pump 4, high-pressure pump 5, low-pressure control valve142 for the high-pressure pump 5, a common rail 6 and an injector 6A.The difference between solenoid valve unit 156 and the solenoid valveunit 141 of FIGS. 11 and 12 is that there is no check valve 144, and adiameter has been selected for the orifice 145 which ensures that theset opening pressure of the low-pressure control valve 142 exceeds thehigh-pressure passage 21 pressure when the solenoid valve 143 is open(on). The solenoid valve unit 156 thus configured provides the sameeffects as those of the solenoid valve unit 141 as shown in FIG. 13, sosubstantially the same description thereof applies and therefore may beomitted here.

If the diameter of the orifice 145 is increased, it is necessary toincrease the strength of the solenoid spring 150 used in the solenoidvalve 143, which is to say it is necessary to use a stronger (larger)solenoid valve 143. As such, there is a limit to the extent that justthe diameter of the orifice 145 can be used to provide the low-pressurecontrol valve 142 with an opening pressure that is greater than thepressure of the high-pressure passage 21. Beyond that limit, it isnecessary to use a solenoid valve unit 141 provided with a check valve144, as in the arrangement illustrated by FIGS. 11 and 12.

A solenoid valve unit 160 of a sixth embodiment according to the fourthaspect of the invention will now be described with reference to FIG. 17.This embodiment is characterized in that the solenoid valve 143 andhigh-pressure control valve 7 portions of the preceding embodiment (thesecond aspect of the invention) are integrated. FIG. 17 is a sectionalview of the solenoid valve unit 160, which is provided with a checkvalve 144 and a solenoid valve 161 in a valve unit housing 20. Thesolenoid valve unit 141 (FIG. 12) and high-pressure control valve 7 ofthe fourth embodiment are integrated together in the case of thesolenoid valve 161, which has a needle valve 162 which integrates anarmature damper portion 162A, a valve element portion 162B and a damperportion 162C. In the needle valve 162, the valve element 23 of thehigh-pressure control valve 7 and the armature 148 and element 153 ofthe solenoid valve 143 are integrated and used in common.

The armature portion 162A receives the action of the solenoid 151 andthe solenoid spring 150 and the valve element portion 162B receives theaction of the pressure adjustment spring 25, to thereby open and closecommunication between the high-pressure passage 21 and the low-pressurepassage 22. A damping effect is produced by the sliding movement of thedamper portion 162C in a cavity 24A in the valve seat member 24. Thesolenoid spring 150 may be omitted by setting the force of the spring 25at an appropriate level. With the solenoid valve unit 160 thusconfigured, switching the solenoid 151 on causes the armature portion162A to be drawn upwards, with reference to the drawing, lifting thevalve element portion 162B off the valve seat member 24 and therebyopening communication between the high-pressure passage 21 andlow-pressure passage 22.

Thus, as in the case of the solenoid valve unit 141, during enginestartup a prescribed amount of fuel can be supplied to the common rail 6and injector 6A by the low-pressure pump 4 instead of the high-pressurepump 5. Switching the solenoid 151 off causes the valve element portion162B to be seated on the valve seat member 24, closing communicationbetween the high-pressure passage 21 and low-pressure passage 22. Thesame function as that of the high-pressure control valve 7 can berealized by opening and closing the valve element portion 162B accordingto the opening pressure of the spring 25 and the fuel pressure.

With respect to the operation of the needle valve 162 thus configured,transitory or abnormal variations in the pressure of the fuel from thehigh-pressure passage 21 can be damped and overshoot and undershootprevented by the damper portion 162C sliding in the cavity 24A while aprescribed oil-tightness is maintained, imparting the type of stabilityprovided by a high-pressure control valve 7. In this embodiment thedamper portion 162C is arranged on the high-pressure passage 21 side,i.e. the high-pressure side. However, it can also be arranged on thelow-pressure passage 22 side, i.e. the low-pressure side.

FIG. 18 is a sectional view of a solenoid valve unit 170 with a solenoidvalve 171 and a damper portion provided on the low-pressure side,according to a seventh embodiment. The solenoid valve 171 has a valveseat member 172 corresponding to the valve seat member 24, a needlevalve 173 corresponding to the needle valve 162, and a pressureadjustment spring 174 corresponding to the spring 25 and solenoid spring150. Integrally formed in the needle valve 173 are a portion 173A inwhich armature and damper portions are integrated, and a valve elementportion 173B that is seated on the valve seat member 172. The damperportion 173A slides vertically within a cylindrical member 175. With thesolenoid valve unit 171 thus configured, switching the solenoid 151 oncauses the armature damper portion 173A to be drawn upwards, withreference to the drawing, lifting the valve element portion 173B awayfrom the valve seat member 172, thereby opening communication betweenthe high-pressure passage 21 and low-pressure passage 22.

Thus, as in the case of the solenoid valve unit 141, during enginestartup the required amount of fuel can be supplied to the common rail 6and injector 6A by the low-pressure pump 4 instead of the high-pressurepump 5. Switching the solenoid 151 off causes the valve element portion173B to be seated on the valve seat member 172, closing communicationbetween the high-pressure passage 21 and low-pressure passage 22. Thesame function as that of the high-pressure control valve 7 can berealized by opening and closing the valve element portion 173B accordingto the opening pressure of the spring 174 and the fuel pressure. Thecheck valve 144 may be omitted, as in the third aspect of the invention,by optionally setting the diameter of the orifice 145 opened and closedby the valve element portion 173B.

With respect to the operation of the needle valve 173 thus configured,transitory or abnormal variations in the pressure of the fuel from thehigh-pressure passage 21 can be damped and overshoot and undershootprevented by the armature damper portion 173A sliding in the cylindricalportion 175 while a prescribed oil-tightness is maintained, impartingthe type of stability provided by a high-pressure control valve 7. Thesolenoid valve 171 thus configured according to the seventh embodimentprovides the effects of the high-pressure control valve 7 and solenoidvalve 143 while also providing the same damper effect as that of thesolenoid valve 161 of the sixth embodiment (FIG. 17).

The damping effect can be increased by using a flat plate shaped valveelement 176, such as the one shown in FIG. 19, instead of the rod shapedtypes of needle valves 162 and 173. The valve element 176 is constitutedby a portion 176A formed by integrating a flat plate shaped armatureportion and a peripheral flange shaped damper portion, and a conicalvalve element 176B that seats on a valve seat portion 177 that opensinto the high-pressure passage 21. The armature damper portion 176Aslides vertically within a solenoid chamber 178.

The damping effect can be increased by increasing the sectional area ofthe armature damper portion 176A used as the armature. Using aconfiguration in which the solenoid valve 143 and high-pressure controlvalve 7 portions are integrated as in the solenoid valve 161 andsolenoid valve 171 will mean there is just one seat portion, as in thecase of valve seat member 24 (FIG. 17) and valve seat member 172 (FIG.18). As shown by FIG. 20, the result is that even with a low flow rate,there is no decline in the control pressure of solenoid valves 161 and171 (indicated by the solid line), so a constant pressure can bemaintained.

As described in the foregoing, in the solenoid valve unit according tothe present invention, during engine startup fuel is delivered to theinjector under low pressure by a low-pressure pump. This prevents fuelvaporization during hot restarts and enables high-pressure fuel deliveryby the high-pressure pump during normal high-pressure engine operation.The result is that stable engine operation can be achieved.

Furthermore, according to the first aspect of the invention, even whenjust one solenoid valve is used, two passages can be controlled, one onthe high-pressure side of the pressure control valve and the other onthe return port side. Such a configuration allows costs to be reducedand high pressures to be controlled by a small force, ensuring reliableopening and closing of the passages.

In another embodiment according to the second aspect of the invention,in which a check valve is used, the low-pressure control valve of thehigh-pressure pump is given a higher opening pressure than that of thecheck valve, so that even after the engine has been started and isoperating normally, by controlling the solenoid valve, it is possible touse high-pressure or low-pressure fuel delivery as required. In anotherembodiment according to the third aspect of the invention, in which anorifice is used instead of a check valve, the same effect is obtained bysetting the orifice to an appropriate size.

A further arrangement according to the fourth aspect of the invention inwhich the high-pressure control valve and the solenoid valve areintegrated helps to reduce costs, decrease the overall size and providehigher reliability.

What is claimed is:
 1. A fuel injection apparatus comprising:alow-pressure pump that supplies fuel at low pressure from a fuel tank,an injector, a high-pressure pump that is connected with and thatreceives the low-pressure fuel from the low-pressure pump and thatsupplies the fuel at high pressure to the injector that injects the fuelat high pressure into an engine, a solenoid valve unit comprising: aunit housing provided with a high-pressure lead-in port from theinjector, a low-pressure lead-out port to the fuel tank, a return portfrom the high-pressure pump, a high-pressure passage in communicationwith the lead-in port, a low-pressure passage in communication with thelead-out port, and a return port passage in communication with thereturn port, a pressure control valve that opens and closes thehigh-pressure and low-pressure passage in accordance with pressure atthe lead-in port, and solenoid valves able to communicate with thelead-in port and lead-out port via the pressure control valve and ableto open and close communication between the high-pressure passage andthe low-pressure passage, and between the low-pressure passage and thereturn port passage, wherein the solenoid valves are controlled to opencommunication between the high-pressure passage and the low-pressurepassage and close communication between the low-pressure passage and thereturn port passage during engine startup, and to close communicationbetween the high-pressure passage and the low-pressure passage, and opencommunication between the low-pressure passage and the return portpassage during normal engine operation.
 2. An apparatus according toclaim 1 wherein the solenoid valves comprise a first solenoid valve thatopens and closes communication between the high-pressure passage and thelow-pressure passage and a second solenoid valve that opens and closescommunication between the low-pressure passage and the return portpassage.
 3. An apparatus according to claim 2 wherein after the engineis operating normally, the solenoid valves are such that communicationbetween the high-pressure passage and the low-pressure passage is closedby setting the first solenoid valve to off and communication between thelow-pressure passage and the return port passage is opened by settingthe second solenoid valve to off.
 4. An apparatus according to claim 2wherein after the engine is operating normally, the solenoid valves aresuch that communication between the high-pressure passage and thelow-pressure passage is closed by setting the first solenoid valve to onand communication between the low-pressure passage and the return portpassage is opened by setting the second solenoid valve to off.
 5. Anapparatus according to claim 2 wherein the first solenoid valve and thesecond solenoid valve both have the same configuration.
 6. An apparatusaccording to claim 1 wherein the solenoid valve uses a single armatureto drive a first valve element that opens and closes communicationbetween the high-pressure passage and the low-pressure passage and asecond valve element that opens and closes communication between thelow-pressure passage and the return port passage.
 7. An apparatusaccording to claim 6 wherein after the engine is operating normallycommunication between the high-pressure passage and the low-pressurepassage is closed and communication between the low-pressure passage andthe return port passage is opened by setting the solenoid valve to on.8. An apparatus according to claim 6 wherein there is a valve seatmember that is provided with a connecting rod that connects the firstvalve element with the second valve element and in which are formed afirst seat face for the first valve element, a second seat face for thesecond valve element, and a connecting passage that can providecommunication between the high-pressure passage and the low-pressurepassage, and between the return port passage and the low-pressurepassage.
 9. A fuel injection apparatus comprising:a low-pressure pumpthat supplies fuel at low pressure from a fuel tank, an injector, ahigh-pressure pump that is connected with and that receives thelow-pressure fuel from the low-pressure pump and that supplies the fuelat high pressure to the injector that injects the fuel at high pressureinto an engine, a solenoid valve unit comprising: a unit housingprovided with a high-pressure lead-in port from the injector, alow-pressure lead-out port to the fuel tank, a high-pressure passage incommunication with the lead-in port, and a low pressure passage incommunication with the lead-out port, a high-pressure control valve thatopens and closes the high-pressure passage and low-pressure passage inaccordance with pressure at the lead-in port, a solenoid valve that isable to communicate with the lead-in port and lead-out port via thehigh-pressure control valve and can open and close communication betweenthe high-pressure passage and the low pressure passage, a check valvearranged between the low-pressure passage and the fuel tank, and alow-pressure control valve arranged between the high-pressure pump andthe fuel tank, wherein an opening pressure of the low-pressure controlvalve is set at a higher pressure than the valve opening pressure of thecheck valve and the solenoid valve is controlled to open communicationbetween the high-pressure passage and the low-pressure passage duringengine startup, and to close communication between the high-pressurepassage and the low-pressure passage during normal engine operation. 10.An apparatus according to claim 9 wherein the low-pressure control valveis arranged closer to the fuel tank than the check valve is to the fueltank.
 11. A fuel injection apparatus comprising:a low-pressure pump thatsupplies fuel at low pressure from a fuel tank, an injector, ahigh-pressure pump that is connected with and that receives thelow-pressure fuel from the low-pressure pump and that supplies the fuelat high pressure to the injector that injects the fuel at high pressureinto an engine, a solenoid valve unit comprising: a unit housingprovided with a high-pressure lead-in port from the injector, alow-pressure lead-out port to the fuel tank, a high-pressure passage incommunication with the lead-in port, and a low pressure passage incommunication with the lead-out port, .Iadd.said high-pressure passagehaving an orifice formed therein,.Iaddend. a high-pressure control valvethat opens and closes the high-pressure passage and low-pressure passagein accordance with pressure at the lead-in port, a solenoid valve thatis able to communicate with the lead-in port and lead-out port via thepressure control valve and can open and close communication between thehigh-pressure passage and the low-pressure passage, and a low-pressurecontrol valve arranged between the high-pressure pump and fuel tank,wherein the orifice in the high-pressure passage is of a diameter thatallows the valve opening pressure of the low-pressure control valve tobe set at a higher pressure than the pressure in the high-pressurepassage when the solenoid valve is set at open and the solenoid valve iscontrolled to open communication between the high-pressure passage andthe low-pressure passage during engine startup, and to closecommunication between the high-pressure passage and the low-pressurepassage during normal engine operation.
 12. An apparatus according toclaim 11 wherein the low-pressure control valve is arranged closer tothe fuel tank than the orifice is to the fuel tank.
 13. A fuel injectionapparatus comprising:a low-pressure pump that supplies fuel at lowpressure from a fuel tank, an injector, a high-pressure pump that isconnected with and that receives the low-pressure fuel from thelow-pressure pump and that supplies the fuel at high pressure to theinjector that injects the fuel at high pressure into an engine, asolenoid valve unit comprising: a unit housing provided with ahigh-pressure lead-in port from the injector, a low-pressure lead-outport to the fuel tank, a high-pressure passage in communication with thelead-in port, and a low-pressure passage in communication with thelead-out port, . .said high-pressure passage having an orifice formedtherein,.!. a high-pressure control valve that opens and closes thehigh-pressure passage and low-pressure passage in accordance withpressure at the lead-in port, and a solenoid valve that can open andclose communication between the high-pressure passage and thelow-pressure passage, wherein the solenoid valve and the high-pressurecontrol valve are integrated by making common use of a valve elementthereof.
 14. An apparatus according to any of claims 1, . .9, 11.!. or13 wherein the high-pressure control valve. ., each of.!. .Iadd.and.Iaddend.the solenoid . .valves and the check valve and orifice.!..Iadd.valve .Iaddend.are formed in a single unit housing.
 15. Anapparatus according to claim 13 wherein a damper portion is formed onthe low-pressure side of the solenoid valve.
 16. An apparatus accordingto claim 15 wherein the solenoid valve is provided with an armaturedamper portion that slides vertically within a cylinder and a valveelement portion that seats on a valve seat member opening to thehigh-pressure passage.
 17. An apparatus according to claim 13 wherein adamper portion is formed on the high-pressure side of the solenoidvalve.
 18. An apparatus according to claim 17 wherein the solenoid valveis provided with a needle valve in which are integrated a damper portionon the high-pressure side that slides within a cavity in the valve seatmember, an armature portion, and a valve element portion that seats onthe valve seat member opening to the high-pressure passage.
 19. Anapparatus according to claim 13 wherein the solenoid valve and thehigh-pressure control valve body are formed as a flat plate shaped valveelement.
 20. An apparatus according to claim 19 wherein the flat plateshaped valve element is provided with an armature damper portion thatslides vertically along the inner wall of a solenoid chamber formed inthe unit housing, and a valve element portion that seats on a valve seatmember opening to the high-pressure passage.
 21. An apparatus accordingto claim 13 wherein the solenoid valve is configured as a high-pressureaction type in which the element can close communication between thehigh-pressure passage and the low-pressure passage when subjected tohigh pressure from the high-pressure passage.
 22. An apparatus accordingto any of claims 9, 11 or 13 wherein the solenoid valve is configured asa high-pressure opposition type in which when the solenoid thereof is inan off state communication between the high-pressure passage and thelow-pressure passage can be closed in opposition to high pressure fromthe high-pressure passage.
 23. An apparatus according to any of claims 9or 11 wherein the high pressure control valve and the solenoid valve arearranged in parallel between the high-pressure lead-in port and thelow-pressure lead-out port.
 24. An apparatus according to any of claims9, 11 or 13 wherein the high-pressure passage and the low-pressurepassage are formed parallel to each other and are straddled by at leastone of the high-pressure control valve and the solenoid valve. .Iadd.25. An apparatus according to claim 9 wherein the check valve is formedin a single unit housing..Iaddend..Iadd.26. An apparatus according toclaim 11 wherein the orifice is formed in a single unithousing..Iaddend..Iadd.27. An apparatus according to claim 13 whereinthe high pressure passage having an orifice which is formed in a singleunit housing..Iaddend.